Alkyltin alkoxides are very useful as catalysts for the synthesis or transesterification of esters or the curing reaction of silicon polymer or urethane.
Currently used processes for production of alkyltin alkoxides include: for example, the process which uses a dialkyldichlorotin as a raw material (see, for example, Patent Reference 1); and the process which uses a dialkyltin oxide as a raw material (see, for example, Patent Reference 2). The former process, which uses a dialkyldichlorotin as a raw material, uses a high-cost metal alcoholate as a secondary material. In addition, it produces two moles of metal salt per one mole of dialkyltin alkoxide, as an aimed product, as shown in the following reaction equation (8), which causes problems of wastes or the like. Thus, use of the former process as an industrial production process still poses problems, including high production cost and waste production.

The latter process, which uses a dialkyltin oxide as a raw material, is preferable in that it does not produce a large amount of wastes. Thus, investigations have been made of producing dialkyltin alkoxides using the latter process. One example of such production processes is such that it produces a dialkyltin alkoxide from dibutyltin oxide and an alcohol by a two-stage reaction, as shown in the following reaction equation (9) (see Patent Reference 3). In the first stage, dibutyltin oxide and an alcohol are allowed to react in benzene or toluene at a temperature in the range of 80° C. to 110° C., followed by removal of formed water by azeotropic distillation, to produce 1,1,3,3-tetrabutyl-1,3-dialkoxy-distannoxane. In the second stage, the above described distannoxane is subjected to disproportionation at a temperature in the range of 180° C. to 220° C., followed by distillation, to produce a dibutyltin dialkoxide. This process is superior in that it does not produce wastes; however, the disproportionation in the second stage of the process involves the distillation of a high boiling point dialkyltin alkoxide under a high temperature, and therefore consuming a significant amount of energy. Thus, use of the latter process as an industrial production process still poses problems, including high energy consumption. Further, the process has a low productivity.

As a process for producing a dialkyltin dialkoxide directly from a dialkyltin oxide and an alcohol, a process is disclosed in which a high boiling point alcohol is used, as shown in the following reaction equation (10) (see Patent Reference 2). In this process, the reaction is performed at a temperature higher than that of the case where the reaction is performed in benzene or toluene, since it is performed at the boiling point of the alcohol as a reactant, followed by removal of the formed water, as an azeotropic mixture of water and alcohol as a reactant. This process is superior to the above described process in that it does not require the heat distillation of a high boiling point dialkyltin dialkoxide. However, since the reaction temperature is the boiling point of the alcohol as a reactant, the reaction rate is low for the alcohols with a small number of carbon atoms and even for the alcohols with a large number of carbon atoms. Thus the process has a low productivity.

Further, in the above described process, since the reaction was performed in a high boiling point alcohol at a high temperature, a large amount of trialkyltin compound, which is probably produced in accordance with the following reaction equation (11), is actually produced. In fact, it is well known that trialkyltin compounds are produced by the pyrolysis of dialkyltin alkoxides (see Non-Patent Reference 1), and the trialkyltin compound may form a complex mixture of reaction by-products, other than the dialkyltin dialkoxide which the present invention is aiming at. Thus, this process is not preferable, either, as an industrial production process.

To increase the productivity, which is one of the problems the above described processes have, there is disclosed a process which uses an alcohol and a carbonate ester as reactants, as shown in the reaction equation (12) (see Patent Reference 2). This process involves the use of high cost carbonate ester as a reactant, though it improves the productivity the above described processes have; thus, use of this process still poses problems, including high production cost.

[Patent Reference 1] U.S. Pat. No. 2,700,675
[Patent Reference 2] U.S. Pat. No. 5,545,600
[Patent Reference 3] NL-6612421
[Non-Patent Reference 1] Journal of the Society of Chemical Industry, 72,7 (1969), 1543